1. Field of the Invention
The present application relates generally to circuit interrupting devices, such as ground fault circuit interrupting (GFCI) devices, that prevent power from being delivered to a connected load when the circuit interrupting device is not properly wired. More particularly, the present application is directed to a latching mechanism provided in a GFCI device that will not enter a latched, “reset,” state connecting a line contact with a load contact unless the GFCI device is properly installed with AC power connected to the line terminals of the device.
2. Description of Related Art
GFCI devices are designed to trip in response to the detection of a ground fault condition at an AC load. Generally, the ground fault condition results when a person comes into contact with the line side of the AC load and earth ground at the same time, a situation that can potentially result in serious injury or death. The GFCI device recognizes this condition by using a sensing transformer to detect an imbalance between the electric currents flowing in the hot and neutral conductors of the AC supply, as will occur when some of the load current is being diverted to ground. When such an imbalance is detected, an actuator, such as a solenoid or a relay, activates a latched circuit breaker mechanism within the GFCI device to enter a tripped state, thereby opening one or both sides of the AC line, i.e., hot and/or neutral, removing power to the load.
GFCI devices may be connected, for example, to fuse boxes or circuit panels, but more commonly, conventional GFCI devices are incorporated into electrical receptacles and installed at various locations within a building. Similar to regular electrical receptacle outlets these conventional GFCI devices have a set of conductive receptacle terminals that are accessible through slots in the face of the GFCI device. In many GFCI devices these face terminals are connected directly to the load terminals which are electrically connected to the line terminals when the latching mechanism is in a closed, or reset, condition. When the device is properly wired the AC power source is connected to the line terminals of the GFCI device and downstream load devices, such as additional GFCI devices or regular, non-GFCI, receptacles, are electrically connected to the load terminals.
If the GFCI device is “reverse wired,” also referred to as “miswired,” where the AC power source is connected to the load terminals instead of the line terminals, a potentially dangerous situation arises. That is, according to some conventional GFCI devices, when the load terminals are connected to an AC power source, and the receptacle, or face, terminals are electrically connected to the load terminals, the receptacle terminals are always powered, even if the circuit breaker, or latching mechanism, is not latched. As a result, the installer, and possibly the user, would be under the mistaken impression that the GFCI is operating correctly. The installer or user would be unaware that the GFCI is not providing fault protection, even when a fault condition is detected and the device trips, as expected. That is, if the device trips, for example in response to a real or test ground fault, power is still supplied to the face terminals and any device plugged into the face terminals. This is because AC power is directly connected to the load terminals which, in many older devices, are electrically connected to the face terminals.
To prevent such a potentially dangerous situation, Underwriters Laboratories (UL) Standard 943 requires that GFCI devices have a means to detect such miswiring conditions, and prevent power from being supplied to the face terminals in such instances. Thus, in accordance with UL standards, any attempt to reset a miswired GFCI device should prevent power from being provided to the face terminals. A solution employed by some manufacturers is to provide the GFCI to the installer in a tripped condition where the latch mechanism is in an open, unlatched, state such that no power is provided to the face terminals. The latch mechanism is then permitted to enter a closed, reset, state only if the device is properly wired. These types of GFCI devices typically utilize a mechanical locking mechanism that prevents the device from being reset until a properly wired condition is detected, at which point the locking feature is disabled. The locking feature of these GFCI devices is typically permanently disabled after the device is properly installed. Thus, according to these devices miswiring protection is only provided at the time of initial installation. This solution is particularly undesirable because the GFCI device no longer provides miswiring protection when the GFCI device is removed and/or re-installed later.
Another undesirable characteristic of such devices is the propensity for the mechanical locking feature to malfunction due to something happening to the device prior to the first installation. Known causes of such malfunction include the device being subjected to strong vibrations or shock during shipping, for example, resulting from the device being dropped, or otherwise exposing the GFCI device to an impact. In this case, the face terminals will provide unprotected power unbeknownst to the user if the GFCI device is miswired.
Further, it is known that even though manufacturers typically advise customers and the public to test their GFCI devices periodically by pressing the “TEST” button on the device, causing an intentional imbalance in the hot and neutral currents in the device, the devices are rarely tested as advised. Accordingly, some manufacturers have provided so-called “self-test” mechanisms within their GFCI devices for automatically testing the device without requiring human intervention. Conventional self-test GFCI devices, however, fail to test the device in a robust fashion where many of the device components are tested and false failures are ignored.
Thus, it is desirable to provide a GFCI device that includes shock and/or drop proof miswiring protection, which is re-installable after the device has been removed or power has been cut-off from the device and which optionally provides a robust self-testing feature for automatically testing the functionality of the device without human intervention.